1. Field of the Invention
The present invention relates generally to the field of semiconductor devices, and more particularly to a method of fabricating a semiconductor structure having a metal electrode and a self-aligned contact (SAC).
2. Description of the Prior Art
Along with the continuous miniaturization of the Integrated Circuits (IC), the feature sizes of semiconductor devices within the ICs are also scaled down continuously. In order to overcome electrical or processing limitations arising from the miniaturization of semiconductor devices, semiconductor manufacturers have found several solutions. For example, for a transistor device with a polysilicon gate, some disadvantages, such as boron penetration and depletion effect often occur and cause inferior performance of the transistor device. In order to solve these drawbacks, some semiconductor manufacturers adopt a gate-last process to replace the conventional polysilicon gate with a metal gate having metal electrode. Additionally, along with the shrinkage between two adjacent gate structures, semiconductor manufacturers also correspondingly invent a method for self-aligning a contact structure so as to overcome drawbacks due to the insufficient space between the two adjacent gate structures.
For a transistor device having both the metal gate and the self-aligned contact structure, a mask layer is often formed to cover the metal gate prior to the formation of the self-aligned contact structure. In the case where the gate electrode is covered by the mask layer, even though the self-aligned contact structure is formed close to the metal gate, there is still no unnecessary contact between them.
However, even though the above-mentioned self-aligned contact structure is widely used to present unnecessary electrical connection, there is still a problem that needs to be overcome. For example, because the width of the mask layer is often equal to or less than the width of the underlying metal gate electrode, the self-aligned contact structure is still able to be in direct contact with the lateral of the adjacent metal gate electrode during the process of forming the self-aligned contact structure.
Accordingly, in order to overcome the above-mentioned problem, there is still a need to provide a method of fabricating a semiconductor structure having a metal gate and a self-aligned contact structure.